Process for reducing the quantity of thiophenes in an aromatic hydrocarbon



Aug. 9, 1960 Filed July 25, 1958 THIOPENE CONTENT Mg per Kq Benzene A.P. OELE ETAL 2,948,764 PROCESS FOR REDUCING THE QUANTITY OF THIOPHENESIN AN AROMATIC HYDROCARBON 2 Sheets-Sheet 1 120 150 200 240 280 320PULSATIONS (Pulses per minute) 4o'eo are/rm P. OELE,

mam/n5 Ia. muYTJENs DTTDPNEYS and Aug. 9, 1960 A. P. OELE EI'AL2,948,764

PROCESS FOR REDUCING THE QUANTITY OF THIOPHENES m AN AROMATICHYDROCARBON Filed'July 25, 1958 2 Sheets-Sheet 2 DISTRIBUTOR BAFFLESTAKE OFF ,1-COLUMN BUFFER TANK SEPARATING VESSEL SPENT LIQUOR STORAGETANK VESSEL nvmnnu P. 051.5,

HTTOYIYE Y5 PROCESS FOR REDUCING THE QUANTITY OF 'I'I(-)I)PI IENES IN ANAROMATIC HYDROCAR- B Adriaan P. Oele, Mathias J. G. Muytjens, and JohanR. 'H. Goris, all of Geleen, Netherlands, assignors to Stamicarbon N.V.,Heerlen, Netherlands This invention relates to the treatment of aromatic"United Stat a ent-Q hydrocarbons with sulphuric acid for the removal ofthiophenes.

Crude benzene and benzene homologues may be obtained by washing cokeoven 'gas with a tar oil and subsequently steam distilling the tar oilto free the same from the mixture of aromatic hydrocarbons absorbed bythefoil in the washing step. The absorbed mixture of hydocarbons mainlyconsists of benzene, toluene and xylene, but also contains various othersubstances such as cyclopentadiene. A further purification of 'themixture of aromatic hydrocarbons is effected by rectification whereby,in addition to cyclopentadiene obtained in the first runnings, fractionsconsisting of benzene, toluene and xylene are obtained.

The abovementioned fractions containing benzene undesirable impuritiesthat they are unsuitable for many purposes, e.g., for use as motor fuel.Along with unsaturated compounds, which tend to cause gumming anddiscoloration, these fractions contain orgganic sulphur compounds, suchas thiophene and methyl thiopene.

It is customary to remove the unsaturated compounds by treating theimpure benzene, toluene and/0r xylene with more or less concentratedsulphuric acid, e.g., 80- 96% sulphuric acid by weight. This treatment,which and/ or its homologues are so strongly contaminated with V may becarried out either discontinuously in stirring vessels, or continuously,e.-g. in a packed column in which 5 the impure aromatic hydrocarbons andthe sulphuric acid are contacted while flowing in counter-currentrelation, results in the conversion of theunsaturated impurities intoproducts of higher molecular weight. These high molecular weightproducts form, together with the sulphuric acid, a so-called acid tarWhich may be separated from the benzene and its homologues. The thuspurified benzene and benzene homologues are then subjected to washingwith caustic soda and again distilled.

The above described treatment with sulphuric .acid leaves much to bedesired in the way of simplicity of operations, cost, reduction ofthiophene content and the like. Accordingly, the principal object of thepresent invention is .to provide novel-improvements in thecontinuous-type of process referred to above whereby the quantity ofthiophenes in aromatic hydrocarbons may be effectively reduced bytreating the same with sulphuric acid. Other objects will also beapparent from the following description of the invention. 1 Broadlystated, the improved process of the present invention comprises passingthe sulphuricacid and the hydrocarbon liquid continuously and, incountercurrent through .a vertical column filledwith packing bodies, thehydrocarbon liquid being passed upwardly through the column, andpulsating the liquids. during their passage through the column. I i e VThe extentto which the thiophene content-of-a hydrocarbon is reduced bycountercurrent treatment with ice . 2 strength of the sulphuric acid andthe quantities of hydrocarbon and sulphuric acid passing in contact perunit time. However, other things being equal, the step'jof impartingpulsations to the liquid, according to the present invention, has beenfound to lead to a significant improvement in the thiophene removal.Moreover with appropriate choice of the acid strength and othertreatmentconditions, including the frequency of the pulsations and the ratio ofhydrocarbon to sulphuric acid flowing in countercurrent contact, thethiophenercontent can be reduced to a greater extent with the presentinvention than is possible when carrying out the acid treatment inaccordance with the known techniques described.

above. Thus, for example, by a continuous process according to thepresent invention, it is possible to reduce the thiophene content ofbenzene containing as much as 6500 mg. of thiophene per kg. of benzene,'to below 13 mg. per kg. of benzene, using sulphuric acidwith aconcentration of 95% by weight. Hitherto it has only been possible toreduce the thiophene content of benzene or benzene homologuesto anequivalent extent by treating the hydrocarbon discontinuously in stages,e.g., in two stages, with sulphuric acid, using very highly concentratedsulphuric acid having a strength of 99.5%: by weight, in each stage.Discontinuous processes are laborious and cumbersome, particularlyiflarge quantities of hydrocarbon are to be treated. Furthermore,apparatus for such discontinuous operations takes up a considerableamount of space and it is also essential to use a large quantity ofenergy to disperse the sulphuric acid in the material to be purifiedBatch treatment is also relatively costly in sulphuric acid, as acid. ofthe same strength must be used in each stage. Another, disadvantage ofthe prior procedure is that an appreciable amount of benzene issulphonatedand thuslost.

In order to prevent fouling of the packing bodies in the .column whenoperating according to the present invention, the aromatic hydrocarbonmay be subjected to a pro-purification in .a preceding stage in the formof a treatment with sulphuric acid, the acid being dispersed in thehydrocarbon by mechanical means. .Whether. it isadvantageous to carryout such a pre-purificationde: pends on the nature of the impurity andthedegree-to which the hydrocarbon to be purified is contaminated. If,for example, the hydrocarboncontains about 1 gram of cyclopentadiene perkg., pre-purification is advisable since cyclopentadiene forms an acidtar which'is insoluble in sulphuric acid. i The sulphuric acid used inthe countercur'rent washing of the present process preferably has aconcentration of 95% by weight or more. If a pre-purificationisperformed, the sulphuric acid used for such 1 pretreatment need not haveas high a concentration as that supplied to the washing column. 7 tionof from 75-95% is sufficient for the pretreatment. Thus, acid previouslyused in the countercurrent washing column, combined if necessary withfresh acid makeup, may be effectively usedasthe-pretreating acid. Thepulsation rate influences the degree to which thiophenes are removed andthe resultsobtainable with a given pulsation depend in part on thedimensionsof the; column. In order to reduce the quantity of thiophenesto less than 13 mg. of thiophenes per kgof hydrocarbon, using a washingcolumn of normal commercial .dimensions (e.g., 5-10 metres in height andapproximately 0.25

. v to 2 metres in width or diameter), the liquids are prefer.-

sulp u iq a d d p n s on var act in lu ing. he

For example, an acid concentra- It has previously been proposed tocountercurr'ently con a tbenzeneand sulphuric acid inlahorizontaliapparatus, while imparting pulsations to the contents of the apparatus(British patent Specification No. 404,005). According to said Britishpatent, the apparatus is divided into a series of compartments in such away that separation between benzene and sulphuric acid takes place in anumber of these compartments due to the difference in specific gravity,while in adjoining compartments, the sulphuric acid is mixed again withthe benzene as a result of the pulsation. However, it is not possible toremove thiophenes from the hydrocarbon to any substantial degree by theprocess described in this patent. In other words, it is critical to thesuccess of the present process that the countercurrent hydrocarbon acidcontact take place in a packed vertical column with the hydrocarbonpassing upwardly through a column. The vertical column used in theinvention described herein may be packed with any conventional packingbodies, typically Raschig rings, Berl saddles, or the like.

To prevent or reduce the deposition of acid tar on the packing bodies,the use of glazed porcelain packing bodies is recommended. As thesebodies are considerably more expensive than unglazed porcelain packingbodies, it is advantageous to fill only the bottom part of the column,i.e., about one-third of the column length, with glazed packing bodies.The remainder of the column can be filled with unglazed packing bodiessince deposition of acid tar only occurs in the bottom part of thecolumn. Acid tar deposition may also be reduced or avoided if packingbodies in the form of unglazed packing rings are employed, the rings inthe bottom part of the column having a relatively large diameter. Thus,for example, it is suitable to use 1" rings in the bottom third of thecolumn length and .6" rings in the remaining part of the column. Thepacking bodies may comprise some other material than porcelain, e.g., ametal or metal alloy not attacked by concentrated sulphuric acid and/oracid tar.

If after a certain period of use the packing bodies should show somefouling, they may be cleaned by simply stopping the supply of benzeneand continuing the sulphuric acid supply and the pulsation. The packingbodies may alternatively be cleaned with water, steam or an alkalinesolution. It is also advantageous to place in the column somere-distributors, e.g. baflles, pans or the like on which the aciddescending in the form of drops or a film is collected and automaticallyre-distributed over the packing bodies. In this way, possiblydetrimental wall effects and channelling may be counteracted.

Preferably the packing bodies used herein are of such construction thatthe free space in the packed column amounts to 50-96% of the spaceoccupied by the packing bodies. It is also preferable to pass thebenzene or benzene homologues to be purified through the washingcolumnas a continuous phase, i.e., in the form of an uninterrupted film orcurrent while the sulphuric acid is distributed over the packing bodiesas a discontinuous phase. When operating in this fashion, the sulphuricacid film is partly divided into drops as a result of the pulsation.

It is also possible to have the benzene or homologue thereof dispersedin drops, rising as the discontinuous phase through the sulphuric acidwith the latter forming the continuous phase. With benzene as thecontinuous phase, however, the stroke of the pulsation may be greaterand in order to obtain thorough removal of thiophenes, it is advisableto use the largest possible liquid displacement per pulsation. While theliquid volume displaced by the pulsatiqns is, for a given plunger area,de= pendent on pulsation frequency and the stroke of the plungereffecting the pulsation, there is a limit to the volumetricdisplacement, viz. that displacement at which the packing bodies beginto move, and this happens sooner if the continuous phase is formed bythe sulphuric acid.

The graph constituting Figure l of the accompanying drawing shows therelationship between the degree of thiophene removal and the frequencyvof the pulsations. The influencesof the amount of; benzene or the likefed to the column and the volume displaced by the pulsations are alsoshown.

Referring more particularly to Figure 1, the curves shown therein allrelate to the purification of benzene containing 6500 mg. of thiopheneper kg. of benzene. The treatment was carried out with 4% by volume ofby weight; sulphuric acid in a column having a diameter of 10 cm.,filled to a length of 6.8 metres with A Berl saddles. Nopre-purification was employed. The temperature in the column wasmaintained at 18 C. The benzene was fed upwardly through the column as acontinuous phase while the acid was in the discontinuous phase.

As indicated, the thiophene content of the purified benzene is shown onthe ordinate (logarithmic scale) while the abscissa shows. the pulsationfrequency in pulses per minute, the latter corresponding with the numberof revolutions per minute of the crank shaft actuating the pulsator.

In the tests represented by curves A and A the volume displaced by thepulsations was 600 litres per hour with A and A: litre of benzene,respectively, being supplied per hour and per sq. cm. of the columnsection.

In the cases represented by curves B and B the same amounts of benzeneas for A and A respectively, were supplied but the volume displaced bythe pulsations was 300 litres per hour. It will be noted that the largervolume displacement effected a substantially greater thiophene removaland in each case the amount of thiophene removed was greatest in thefrequency range m 300 pulses per minute.

The temperature utilized for contacting the acid and hydrocarbon may bevaried but should be kept below about 45 C., otherwise an undesirablylarge quantity of the hydrocarbon to be purified may be lost due tosulphona; tion. Usually, a temperature range of about 20 to about 40 C.,is preferred.

The amount of benzene or the like fed to the washing column can berather widely varied and depends upon such factors as the temperatureutilized, the amount of acid and the like. Usually, the higher thetemperature, the greater. the amount of benzene fed to the column,Typically, at a temperature of about 40 C., and an acid supply of 4% byvolume (based on the volume of hen zene) of 95% by weight sulphuricacid, a desirable benzene supply may be 1.5 litres per sq. cm. of thecolumn section. If a stronger sulphuric acid, for example, 99% by weightis used, the supply of benzene may in this case amount to 2.5 litres perhour and per sq. cm. of the column section. Normally, from 1 to 3 litresof benzene or the like per hour. and per sq. cm. of column section canbe treated according to the invention. The data tabulated in Figure 1and the specific reaction conditions set forth above are based on theuse of a column about 7 metres in length. If a longer column is used,the load may be increased accordingly and other operating con.- ditionsmay also be varied for optimum results.

One way of carrying out the invention is diagrammatically shown inFigure 2. As shown therein, the numeral 1 represents a column which mayhave a typical length and diameter of about 10 metres and 50 cm.,respectively. Three layers of packing bodies, e. g., /2" Raschigrings,are positioned within column 1, these layers being designated as A, Band C. Between adjacent layers are posi tioned re-distributors 2 in theform of bafiies. Column 1 is connected through a conduit 3 with apulsator 4, the latter being, in turn, joined by means of conduit 5 to abuffer tank 6. partly filled with benzene or a benzene homologue.Pulsator 4 may comprise a cylinder wherein a disc 4a is mounted forreciprocal movement on a 4b. Like the buffer vessel 6, pulsator 4 andthe conduits 3 and 5 are filled with benzene or a benzene homologue.

Fresh sulphuric acid is sprayed onto the upper layer C of packing bodiesin the top part ofcolumn l by means ofconduit 13. Spent sulphuricacid-is discharged from the bottom of the column through a conduit 14 toa tank 15. If necessary as, for example, in the case where thehydrocarbons to be purified have a high cyclopentadiene content, thespent sulphuric acid can be pumped from tank 15 through a conduit 16into a mixing vessel 8 equipped with suitable stirring means. Benzene orbenzene homologues may be supplied to mixing vessel 8 through conduit 7.

From mixing vessel 8, the mixture of acid and benzene and/or benzenehomologues flows over into a separating vessel 9, in which the sulphuricacid, with the impurities it has taken up, settles. The top layercomprising the pre-purified hydrocarbon is pumped through conduit intothe bottom part of column 1. The hydrocarbon flows upward through thecolumn as the continuous phase and is discharged through conduit 12' toa. caustic soda washery (not shown) for removal of acid residue.

Column 1 is fitted with a level indicator 17, by means of which theposition of the boundary layer between the hydrocarbon and the spentsulphuric acid collecting in the bottom part of the column is checkedand controlled.

The upper part of column 1 is fitted with a jacket 18 through'whicheither cooling water or hot water may be circulated. Cooling water isused when the benzene and/or benzene homologues to be'purified aresupplied to the column in small quantities or if very strong sulphuricacid (e.g., 99% sulphuric acid) is used. Under other circumstances, thereaction temperature in the column may be raised by passing hot waterthrough the jacket if this is desired. An induction heating spiral 19 isprovided about the outer wall of the column, near the bottom partthereof.

If the hydrocarbon to be purified contains only a small amount ofsubstances forming acid tars, the hydrocarbon can be fed directly intothe column through conduits 7 and 7a without being pre-purified. It isalso possible simultaneously to discharge purified hydrocarbon from thetop of the column through conduit 12 and a less thoroughly purifiedproduct through conduits '20 or 21.

By means of the system illustrated in Figure 2, it will be appreciatedthat impure aromatic hydrocarbons, such as the crude benzene, tolueneand xylene fractions obtained by washing coal gas with tar oil,expelling the absorbed hydrocarbons out of the tar oil and rectifyingthe expelled mixture, can be thoroughly freed of thiophenes. Thus, forexample, the thiophene content of a crude benzene fraction, 5000-9000mg. thiophene per kg. of benzene, can be reduced to less than 13 mg. perkg. of benzene, and usually 1-5 mg./ kg. of benzene, by a processinvolving the following conditions: pre-purifying the crude benzene with1% by volume of fresh acid, or with the spent acid from the washingcolumn; supplying the pretreated benzene to the column at the rate 0154cu. m. per hour; using 3-4% by volume of 98-99% by weight sulphuricacid, calculated on the amount of benzene, a temperature of 30 in thecolumn, a frequency of the pulsator crank shaft of 200 r.p.m., a volumedisplacement of 1.25 litres per stroke, measured in the empty column,the column being 500 mm., with the stroke in the empty column beingabout 6 mm.

Using the conditions outlined in the preceding paragraph, benzene lossamounted to only 1.5%. When the benzene load of the column was reducedto 2.5 m. per

6 hour and the sulphuric acid supply amounted to 45% by volume of98.599.5% by weight sulphuric acid, the thiophene content fell to below0.2 mg. of thiophene per kg. of benzene, while the benzene loss was 2%.

By applying a discharge at /a of the column height via conduit 20 andanother at /3 of the column height through a conduit 21, it is possibleto recover simultaneously benzene containing about 1'1 mg. thiophene perkg., and benzene with about 500 mg. of thiophene per kg., respectively.

It will be appreciated that various modifications may be made in theinvention described herein Without deviating from the scope thereof asset forth in the following claims.

We claim: 1. A process for reducing the quantity of thiophenes in anaromatic hydrocarbon by treatment thereof with sulv phuric acid having aconcentration of at least 95%, said process comprising the steps ofcounter-currently and continuously passing said sulphuric acid and saidhydrocarbon in the liquid state at a temperature between 20 and 45 0.,through a packed vertical column containing solid packing material andhaving a free space therein amounting to from 50 to 96% of the spaceoccupied by the packing, the hydrocarbon being passed upwardly throughsaid column, and pulsating the liquids during their passage through saidcolumn, from 100300 pulses being imparted to the liquids per minute.

2. A process according to claim 1 wherein the hydrocarbon liquid ispretreated prior to being passed into said column by mechanically mixingthe same with sulphuric acid having a concentration between and andallowing the acid to settle out.

3. A process according to claim 2 wherein said pretreatment is carriedout with acid discharged from said column.

4. A process according to claim 1 wherein the hydrocarbon is conductedthrough the column as a continuous phase, and the sulphuric acid as adiscontinuous phase.

5. A process according to claim 1 wherein the bottom part of the columnis filled with glazed packing bodies and the remainder of the column isfilled with unglazed packing bodies.

6. A process according to claim 1 wherein the column has a length ofabout 7 metres, the hydrocarbon to be purified is passed through saidcolumn at the rate of 1.02.5 litres per sq. cm. of the column section;the consumption of sulphuric acid is 3-5% by volume calculated on thevolume of the hydrocarbon; and the pulsation stroke calculated as forthe empty column is about 6 mm.

7. A process according to claim 1 wherein a fraction of the hydrocarbonis discharged at an intermediate position along the column and anotherfraction is discharged at the top thereof.

References Cited in the file of this patent UNITED STATES PATENTS1,991,843 Campbell et al. Feb. 19, 1935 2,396,144 Anderson et a1 Mar. 5,1946 FOREIGN PATENTS 404,005 Great Britain Ian. 1, 1934

1. A PROCESS FOR REDUCING THE QUANTITY OF THIOPHENES IN AN AROMATICHYDROCARBON BY TREATMENT THEREOF WITH SULPHURIC ACID HAVING ACONCENTRATION OF AT LEAST 95%, SAID PROCESS COMPRISING THE STEPS OFCOUNTER-CURRENTLY AND CONTINUOUSLY PASSING SAID SULPHURIC ACID AND SAIDHYDROCARBON IN THE LIQUID STATE AT A TEMPERATUE BETWEEN 20 AND 45*C.,THROUGH A PACKED VERTICAL COLUMN CONTINING SOLID PACKING MATERIAL ANDHAVING A FREE SPACE THEREIN AMOUNTING TO FROM 50 TO 96% OF THE SPACEOCCUPIED BY THE PACKING, THE HYDROCARBON BEING PASSED UPWARDLY THROUGHSAID COLUMN, AND PULSATING THE LIQUIDS DURING THEIR PASSAGE THROUGH SAIDCOLUMN FROM 100-300 PULSES BEING IMPARTED TO THE LIQUID PER MINUTE.